POS0894 COMPARISON OF PULMONARY AND SMALL AIRWAYS FUNCTION BETWEEN IDIOPATHIC INFLAMMATORY MYOPATHIES PATIENTS WITH AND WITHOUT INTERSTITIAL LUNG DISEASE
Authors: P. Panagopoulos, V. E. Georgakopoulou, V. Pezoulas, A. Goules, D. I. Fotiadis, T. Vassilakopoulos, A. Tzioufas
Journal: Annals of the Rheumatic Diseases (2022)

Background Pulmonary manifestations of idiopathic inflammatory myopathies (IIM) include interstitial lung disease (ILD) and respiratory muscle weakness, but function of small airways has not been studied in these patients (1). Spirometry, impulse oscillometry and measurement of respiratory resistance by the interrupter technique (Rocc) are tools to evaluate function of small airways. In addition, body plethysmography is the gold standard for measuring lung volumes, whereas nitrogen washout seems impaired, “underestimating” lung volumes in patients with small airways obstruction due to gas trapping (2). Thus, discrepancies between lung volumes measured by those two techniques may be an indication of early small airways dysfunction. Objectives To compare pulmonary and small airways function between IIM patients with and without ILD. Methods This prospective observational study included 13 IIM patients with ILD (8 patients with dermatomyositis and 5 with polymyositis) and 13 IIM patients without ILD (9 patients with dermatomyositis and 4 with polymyositis) who were diagnosed and followed up in the outpatient rheumatology clinic of the Department of Pathophysiology between June and December 2021. All IIM patients fulfilled the 2017 EULAR/ACR classification criteria (3). The presence of ILD was determined by high resolution computed tomography of the lungs that was performed as baseline standard of care at the time of diagnosis and was evaluated by a special radiologist blindly, according to Fleischner Society definitions for ILD (4). Clinical, laboratory and immunological data were recorded at the time of diagnosis and pulmonary function was assessed by spirometry, body plethysmography, single and multiple breath nitrogen washout, impulse oscillometry and measurement of Rocc, diffusing capacity for carbon monoxide (DLco) and maximal inspiratory and expiratory pressures. Statistical analysis for categorical data was performed by Fisher exact test or χ2 square test accordingly and numerical data with Man-Whitney test or t test. Results IIM-ILD patients presented more frequently with dyspnea (53.8% vs 0%, p&lt;0.01), fever (61.5% vs 7.7%, p&lt;0.05) and arthralgias (76.9% vs 23%, p&lt;0.05), compared to IIM patients without ILD. Inflammatory markers, serum muscle enzymes, myositis specific autoantibodies and classic spirometric parameters did not differ between the two groups. IIM-ILD patients had markedly lower predicted DLco compared to those without (mean: 56.3% vs 78.2%, p&lt;0.01). Predicted total lung capacity and residual volume (TLC N2WO %, RV N2WO %) measured by nitrogen washout and the TLC nitrogen washout: TLC body plethysmography ratio (TLC N2WO /TLC pleth ) were significantly lower in IIM-ILD patients compared to those without ILD (mean: 111.1% vs 153.4%, p&lt;0.05, median: 171% vs 210%, p&lt;0.05 and median: 1.28 vs 1.45, p&lt;0.05, respectively). Similarly, ΔΝ2(%) was found significantly higher among non-ILD than ILD-IIM patients [5.4 vs 2.8%, p=0.013]. Predicted normal value of Rocc tended to be higher in IIM-ILD patients, although not statistically significantly. Conclusion Abnormal single breath nitrogen washout and discrepancies between lung volumes measured by body plethysmography and nitrogen washout in IIM-ILD patients, indicate an early small airways dysfunction in these patients. References [1]Selva-O’Callaghan et al. PMID 16130510 [2]Bell et al. PMID 30022817 [3]Lundberg et al. PMID 29079590 [4]Hatabu et al. PMID 32649920 Table 1. Comparison of pulmonary and small airways function variables between IIM patients with and without ILD. Pulmonary function variables IIM-ILD patients (n=13 ) IIM patients without ILD (n=13 ) p value FVC% 88.2 104.1 0.09 FEV1% 85.8 101.9 0.07 FEV1/FVC 82.7 80.9 0.57 FEF 25-75 % 85.7 90.4 0.74 TLC pleth % 82.6 89.9 0.32 RV pleth % 83.9 76.1 0.40 TLC N2WO % 111.1 153.4 0.03 RV N2WO % 171 210 0.039 TLC N2WO /TLC pleth 1.28 1.45 0.039 DLco% 56.3 78.2 0.005 MEP% 69 62.4 0.57 MIP% 93.4 72.5 0.06 ΔN2(%) 2.8 5.4 0.013 Rocc Exp % 100.5 76.6 0.053 R(20)% 99.4 123.4 0.09 Disclosure of Interests None declared